An inherent fault of injecting a polyurethane foam mixture onto a fabric substrate is the penetration of the polyurethane mixture into the fabric due to the high pressure flow of the foam mixture from the mix head during early stages of gelation, and during diffusion of the raw material into the yarn interface by lipophilic or lipophobic properties of the polyurethane material and the yarn. As a result the area of fabric in the impact zone of the polyurethane mix head nozzle is the most susceptible to penetration.
It is common to use a composite layer between the fabric and foam substrates to prevent penetration of the raw materials of the foam composition through the fabric. The composite layer serves the purpose of enhancing the bonding between the mentioned substrates to give good wear resistance properties to the foam and fabric composite while acting as a physical barrier preventing penetration of the raw materials of the foam composition into the fabric. However, a drawback of using such a composite within the substrates is the impaired breathability as a result. For example, this may be the case for automotive seats which will cause an accumulation of heat and moisture between the passenger and the seat, making it very uncomfortable and may even cause damage to the seat over a period of time.
An existing technology in which a composite layer is not used includes the pour-in-place (PIP) technology as described in EP 0210587 and EP 1901828. In the PIP technology which is a non-barrier method, a thin film of PU foam of varying density is used depending on the required breathability and penetration of the product manufactured. The higher the compressed density ratios of PU film the lower the breathability and penetration.
In another method such as that described in U.S. Pat. No. 5,124,368, a temporary barrier is utilised to retard penetration while improving breathability properties. A thermoplastic substrate is introduced as a temporary barrier onto the fabric prior to the foam composition being introduced onto the fabric. Once the foam composition has been exposed to the fabric and curing has taken place, the product is then exposed to high temperatures where the thermoplastic barrier melts. This method, however, does not deliver on expected breathability values and therefore is limited to applications where breathability is not a vital factor. Further, in the case of thinner fabrics, the thermoplastic, once melted, migrates through the fabric and alters the hand feel of the fabric.
Another method is to use an elevated reactive system by employing catalyst to reduce the duration of cream/gel time and cause an exponential rise in the viscosity within that cream time. An example of this method is described in FR 2470566. The inherent rise in viscosity will therefore reduce impact penetration as the foam composition will not be able to pass through the space within the yarns in the fabric. Using such a system to prevent penetration may also reduce reaction times and accelerate curing times, reducing overall cycle times. However, due to this same property of reduced reaction time and accelerated curing time, this system cannot be used to manufacture large articles as creaming and gelling would conclude before the full dosage of the foam composition can be poured and set into the mould. This would leave the product with a ring of layers from the point of pouring outwards with varying density, resilience and uneven curing. A further consequence of using such a method is that elevated levels of catalyst will remain within the finished product. This will cause quality failures due to fogging and staining of the fabric as well as be a health issue if it was to come into contact with the skin.
There is therefore a need for an improved foam composition and method for the manufacturing of a fabric laminated foam article.